Spark plugs can be used to initiate a combustion process in an internal combustion engine. Spark plugs typically ignite a gas, such as an air/fuel mixture, in an engine cylinder or combustion chamber by producing a spark across a spark gap defined between two or more electrodes. Ignition of the gas by the spark causes a combustion reaction in the engine cylinder that is responsible for the power stroke of the engine. The high temperatures, high electrical voltages, rapid repetition of combustion reactions, and the presence of corrosive materials in the combustion gases can create a harsh environment in which the spark plug must function. This harsh environment can contribute to erosion and corrosion of the electrodes that can negatively affect the performance of the spark plug over time, potentially leading to a misfire or some other undesirable condition.
For example, nickel (Ni) and Ni-based alloys, including nickel-iron-chromium alloys like those specified under UNS N06600 and sold under the trade names Inconel 600™, Nicrofer 7615™, and Ferrochronin 600™, are widely used as spark plug electrode materials. However, these materials are susceptible to high temperature oxidation and other degradation phenomena which can result in erosion and corrosion of the electrodes, thus increasing the spark gap between the central electrode and ground electrode. The increased spark gap between the electrodes may eventually induce a misfire of the spark plug.
To reduce erosion and corrosion of the spark plug electrodes, various types of precious metals and their alloys—such as those made from platinum and iridium—have been used. These materials, however, can be costly. Thus, spark plug manufacturers sometimes attempt to minimize the amount of precious metals used with an electrode by using such materials only at a firing tip or spark portion of the electrodes where a spark jumps across a spark gap.